What are HMB Tablets 500mg? BULK POWDERS™ HMB Tablets contain a large 500mg dose of the highest quality & purest HMB available. HMB stands for Beta-Hydroxy Beta-Methylbutyrate & it is a metabolite of the Branched Chain Amino Acid, Leucine. Unfortunately, despite being a metabolite of Leucine, it is not possible to consume vast quantities of Leucine to get the benefits of HMB, as only a tiny amount of Leucine converts to HMB. Research on HMB in the areas of strength, muscle breakdown